This invention relates in general to the construction of heating boilers and in particular to a new and useful heating boiler having axially arranged communicating primary and secondary fire chambers with a fire space wall spaced outwardly from the primary fire chamber having a lining therebetween maintaining a gap between these walls.
Heating boilers of the general type of the present invention are known from German OS. No. 27 21 832 and have proven extraordinarily satisfactory in practice. However, since the wall of the primary fire space is continually cooled from the outside by the cooling water, whereby the marginal flame zone also is considerably cooled, a certain amount of soot is inevitably formed. This may entrail soot deposits in the smoke tubes, which may affect the firing performance of the heating boiler so that in the long run, the waste gas temperatures will increase and such heating boilers will no longer be operable with an optimum efficiency.
The invention is directed to a heating boiler in which the mentioned drawbacks are avoided. Primarily, even after long periods of service, no soot is formed, so as to keep the waste gas temperature constant and substantially improve the long term performance of the heating boiler and to always ensure an optimum efficiency.
In accordance with the invention there is provided a heating boiler which includes an outer housing with a cylindrical wall in the housing extending from one end thereof and defining therewithin a primary fire chamber. A cylindrical fire space wall has a portion which surrounds the cylindrical primary fire chamber wall and is spaced radially outward thereof and has a secondary portion of a greater diameter than the first portion which extends axially beyond the primary fire chamber and defines a secondary fire chamber. The gases which are delivered to the extreme end of the secondary fire chamber pass through one or more conduits which extend through a water space defined between the fire space wall and a corrugated tubular partition wall spaced inwardly of the interior of the housing. The space between the partition wall and the interior of the housing defines a hot water tank. The lining is disposed between the cylindrical wall defining the primary fire chamber and the portion of the fire space wall which is spaced radially outwardly thereof to maintain a clearance gap between these walls which is bridged by the lining itself when the operating temperatures in the furnace are such as to effect this bridging. The cylindrical wall of the fire space is advantageously dimensioned so that as soon as the temperature of the lining attains about 1000.degree. C. the lining applies due to its expansion to the water cooled fire space wall.
On the side adjacent the burner lining is advantageously provided with an outwardly projecting flange which is supported on the fire space wall. The bottom of the lining is advantageously provided with an insulation. The lining is advantageously made of a temperature resistant chromium nickel steel or ceramic material. Conduits which are provided for the conduction of the gases from the secondary combustion space may include turbulators therein which are advantageously of a variable length.
In, accordance ith the invention, a lining closely spaced from the wall of the primary fire space of a heating boiler is inserted, not only optimum combustion values are obtained instantly upon setting the boiler in operation, but also the firing conditions are kept constant for a very long period of time. The lining, initially forming a gap with the surrounding wall of the fire space, is thus heated up within a short period of time to the operating temperature, since it is not cooled optimum combustion conditions are created instantly, without permitting a formation of soot or oil derivatives. Further, since the gap-like clearance is so dimensioned that at a definite temperature of the lining, the lining applies to the water cooled wall of the fire space, it also is ensured that no overheating and no burning through occurs. The lining wall rather expand up to a contact with the wall and then contract again, i.e. it will cyclically expand and contract to give heat off and take it up.
In this way, soot formation which would otherwise be favored by too low temperatures of the fire space wall, is prevented and soot deposits in the heating boiler are avoided. Further, the fire space wall cannot burn through and, primarily, no overheating occurs which might create conditions for the formation of toxic nitrogen oxide gases. A heating boiler designed in this way can always operate with a high efficiency of about 90% and the waste gas temperature remains at a constant low level of about 120.degree. C., so that the waste gas losses are small and excellent combustion results are obtained at all times. Turbulators which may be inserted in the smoke gas tubes remain clean and the gas resistance remains constant. The turbulators produce the effect that more thermal energy is transferred and the performance of the boiler is augmented without the necessity of increasing the waste gas temperature and without clogging the smoke tubes with soot.
Accordingly it is an object of the invention to provide an improved heating boiler which includes primary and secondary fire chambers arranged in axial alignment with the primary fire chamber being formed by an inner wall which is spaced radially inwardly from an outer wall with a lining disposed therebetween containing a gap between these walls and forming a bridge therebetween when the operating temperatures heating the lining to a temperature sufficient to expand it into contact with both walls.
A further object of the invention is to provide a heating boiler which is simple in design, rugged in construction and economical to manufacture.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which a preferred embodiment of the invention is illustrated.